- A
At the Transport layer, the TCP/IP model uses segments, while the OSI model uses packets.
Why wrong: At Transport, the OSI model also uses 'segments' (TCP) or 'datagrams' (UDP); 'packet' is a Network layer term.
- B
In the OSI model, the Network layer encapsulates data into packets, while in the TCP/IP model the Internet layer performs the same function.
Both the OSI Network layer (Layer 3) and TCP/IP Internet layer produce packets (IP packets/datagrams) by adding a Layer 3 header.
- C
The term 'frame' is used at the Data Link layer in both the OSI and TCP/IP models, and it contains the Layer 2 header and trailer.
Frames are the Protocol Data Unit (PDU) at Layer 2, encapsulating the packet with a header and trailer, common to both architectural models.
- D
Encapsulation adds headers and trailers at each layer, so the PDU size decreases as data moves down the stack.
Why wrong: Encapsulation adds headers (and a trailer at Layer 2), causing the overall PDU to grow, not shrink.
- E
The OSI model's Session layer is responsible for end-to-end flow control using TCP segments, while the TCP/IP model combines this into the Application layer.
Why wrong: Flow control is a Transport layer function (Layer 4), not Session (Layer 5). The TCP/IP model has no dedicated Session layer; flow control remains in the Transport layer.
Quick Answer
The correct answer identifies that the term 'frame' is used at the Data Link layer in both the OSI and TCP/IP models, and it contains the Layer 2 header and trailer. This is accurate because during the encapsulation process, as data moves down the stack, each layer adds its own header—and sometimes a trailer—transforming the Protocol Data Unit (PDU) into a new name. Specifically, the OSI Network layer and the TCP/IP Internet layer both encapsulate transport layer segments or datagrams into packets by adding a Layer 3 header, such as an IP header, which applies logical addressing. On the CCNA 200-301 v2 exam, this concept tests your understanding of how PDUs are renamed at each layer, a frequent topic in questions about OSI and TCP/IP encapsulation. A common trap is confusing the PDU names between layers, especially mixing up segments, packets, and frames. Remember the mnemonic: "Please Do Not Throw Sausage Pizza Away" for Physical, Data Link, Network, Transport, Session, Presentation, Application—and that frames live at Layer 2.
CCNA Network Infrastructure and Connectivity Practice Question
This 200-301 practice question tests your understanding of network infrastructure and connectivity. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Which TWO statements accurately describe the encapsulation process and PDU naming across the OSI and TCP/IP models?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
In the OSI model, the Network layer encapsulates data into packets, while in the TCP/IP model the Internet layer performs the same function.
Option B is correct because the OSI Network layer and the TCP/IP Internet layer both encapsulate transport layer segments or datagrams into packets by adding a Layer 3 header (e.g., IP header). This is the fundamental encapsulation step where logical addressing is applied, and the resulting PDU is called a packet in both models. The function is identical despite the different layer names.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
At the Transport layer, the TCP/IP model uses segments, while the OSI model uses packets.
- ✓
In the OSI model, the Network layer encapsulates data into packets, while in the TCP/IP model the Internet layer performs the same function.
Why this is correct
Both the OSI Network layer (Layer 3) and TCP/IP Internet layer produce packets (IP packets/datagrams) by adding a Layer 3 header.
Related concept
Read the scenario before looking for a memorised answer.
- ✓
The term 'frame' is used at the Data Link layer in both the OSI and TCP/IP models, and it contains the Layer 2 header and trailer.
Why this is correct
Frames are the Protocol Data Unit (PDU) at Layer 2, encapsulating the packet with a header and trailer, common to both architectural models.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Encapsulation adds headers and trailers at each layer, so the PDU size decreases as data moves down the stack.
Why it's wrong here
Encapsulation adds headers (and a trailer at Layer 2), causing the overall PDU to grow, not shrink.
- ✗
The OSI model's Session layer is responsible for end-to-end flow control using TCP segments, while the TCP/IP model combines this into the Application layer.
Why it's wrong here
Flow control is a Transport layer function (Layer 4), not Session (Layer 5). The TCP/IP model has no dedicated Session layer; flow control remains in the Transport layer.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓In the OSI model, the Network layer encapsulates data into packets, while in the TCP/IP model the Internet layer performs the same function.Correct answer▾
Why this is correct
Both the OSI Network layer (Layer 3) and TCP/IP Internet layer produce packets (IP packets/datagrams) by adding a Layer 3 header.
✗At the Transport layer, the TCP/IP model uses segments, while the OSI model uses packets.Wrong answer — click to see why▾
Why this is wrong here
Misattributes the 'packet' PDU to the Transport layer – packets are created at the Network layer (Layer 3).
✗Encapsulation adds headers and trailers at each layer, so the PDU size decreases as data moves down the stack.Wrong answer — click to see why▾
Why this is wrong here
Reverses encapsulation logic: each layer adds its own overhead, increasing the size.
✗The OSI model's Session layer is responsible for end-to-end flow control using TCP segments, while the TCP/IP model combines this into the Application layer.Wrong answer — click to see why▾
Why this is wrong here
Incorrectly assigns flow control to the Session layer and misrepresents its placement in the TCP/IP model.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the precise PDU naming per layer (segment, packet, frame) and the fact that encapsulation increases PDU size, not decreases it, to catch candidates who confuse the direction of encapsulation or mix up OSI and TCP/IP layer terminology.
Detailed technical explanation
How to think about this question
In the encapsulation process, each layer adds its own header (and sometimes a trailer, as at Layer 2) to the payload received from the layer above. For example, when TCP hands a segment to IP, IP adds a 20-60 byte header to create a packet; then the Data Link layer adds a 14-byte Ethernet header and a 4-byte FCS trailer to form a frame. This layering ensures modularity and allows protocols like IP to operate independently of the underlying physical medium. In real-world networks, understanding this PDU naming is critical for troubleshooting—e.g., a 'packet drop' at a router refers to Layer 3, while a 'frame error' points to Layer 2 issues.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the 200-301 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this 200-301 question test?
Network Infrastructure and Connectivity — This question tests Network Infrastructure and Connectivity — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: In the OSI model, the Network layer encapsulates data into packets, while in the TCP/IP model the Internet layer performs the same function. — Option B is correct because the OSI Network layer and the TCP/IP Internet layer both encapsulate transport layer segments or datagrams into packets by adding a Layer 3 header (e.g., IP header). This is the fundamental encapsulation step where logical addressing is applied, and the resulting PDU is called a packet in both models. The function is identical despite the different layer names.
What should I do if I get this 200-301 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
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Last reviewed: Jun 25, 2026
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